package br.org.game.nio.core.udp;

import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.net.SocketException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.channels.DatagramChannel;

public class TimeServer {

	private static final int DEFAULT_TIME_PORT = 9090;
	private static final long DIFF_1900 = 2208988800L;

	protected DatagramChannel channel;

	public TimeServer(int port) throws Exception {
		this.channel = DatagramChannel.open();
		this.channel.socket().bind(new InetSocketAddress(port));

		System.out.println("Listening on port " + port + " for time requests");
	}

	public void listen() throws Exception {
		// Allocate a buffer to hold a long value
		ByteBuffer longBuffer = ByteBuffer.allocate(8);

		// Assure big-endian (network) byte order
		longBuffer.order(ByteOrder.BIG_ENDIAN);
		// Zero the whole buffer to be sure
		longBuffer.putLong(0, 0);
		// Position to first byte of the low-order 32 bits
		longBuffer.position(4);
		// Slice the buffer; gives view of the low-order 32 bits
		ByteBuffer buffer = longBuffer.slice();

		while (true) {
			buffer.clear();

			SocketAddress socketAddress = this.channel.receive(buffer);

			if (socketAddress == null) {
				continue; // defensive programming
			}

			// Ignore content of received datagram per RFC 868

			System.out.println(buffer.asCharBuffer().toString());

			buffer.clear(); // sets pos/limit correctly

			// Set 64-bit value; slice buffer sees low 32 bits
			longBuffer.putLong(0, (System.currentTimeMillis() / 1000) + DIFF_1900);

			this.channel.send(buffer, socketAddress);
		}
	}

	// --------------------------------------------------------------

	public static void main(String[] argv) throws Exception {
		int port = DEFAULT_TIME_PORT;

		if (argv.length > 0) {
			port = Integer.parseInt(argv[0]);
		}

		try {
			TimeServer server = new TimeServer(port);

			server.listen();
		} catch (SocketException e) {
			System.out.println("Can't bind to port " + port + ", try a different one");

		}
	}
}
